how to use r_bin_open

[a2ur2]

it's confuse for me to use R_API bool r_bin_open(RBin *bin, const char *file, RBinFileOptions *opt); this c api in r2,i hope to use r2 for my own security tools,but,i got this assert WARN: r_bin_open: assertion 'bin && bin->iob.io && opt' failed (line 231) when i run my the demo in r2-building
code is in here:
int main() {
RBinFileOptions *opt;
RBin *bin = r_bin_new();
r_bin_file_options_init(opt,0,0x400000,0,1);
bin->verbose = false;
ut64 baseaddr = UT64_MAX;
r_bin_file_open (bin, "./afs",opt);
bool isLoaded = r_bin_open (bin, "./afs",opt);
if (isLoaded) {
RListIter *iter;
RBinAddr *ent;
const RList *entries = r_bin_get_entries (bin);
r_list_foreach (entries, iter, ent) {
printf ("-> 0x%"PFMT64x"\n", ent->vaddr);
}
RBinSymbol *sym;
const RList *symbols = r_bin_get_symbols (bin);
r_list_foreach (symbols, iter, sym) {
printf ("-> %s\n", sym->name);
}
}
r_bin_free (bin);
return 0;
}

i hope to get a demo just how to open bin